The invention is directed to weld evaluation, and more particularly to a method and apparatus for non-destructive evaluation of weld integrity.
Testing weld integrity is an important part of many manufacturing processes, such as in automotive manufacturing where spot welds are formed in steel or aluminum sheet metal. Current systems evaluate weld integrity by prying the weld apart, visually inspecting the weld, and measuring the diameter of the weld nugget (e.g., the region where the welding process has formed a true metallurgical bond).
The problem with known evaluation systems, however, is that the weld is destroyed during the evaluation process because the weld must be opened to be visually inspected and measured. Visual inspection also introduces an element of subjective evaluation, creating the potential for inconsistent evaluation results between samples. Further, currently known evaluation methods cannot be automated because they require a great deal of human intervention and/or user input.
There is a need for a system that can conduct non-destructive evaluation of weld integrity and that offers an automation option. There is also a need for a system and method that can evaluate welds using objective criteria to ensure consistent evaluation results between samples.
Accordingly, the present invention is directed to an apparatus and method for non-destructive evaluation of welds. The apparatus generally includes a heater that heats the weld, a camera that detects changes in the surface temperature of the weld, and a computer that acquires and analyzes time-temperature data from the camera as the weld temperature varies over time.
The inventive method includes heating one surface of the sample and starting data collection, in the form of image data, using the camera at the same time the flash begins. The method then includes examining the time-temperature history of individual sections in the image obtained from the camera, such as each pixel in the image. In one embodiment, the method measures heat flux (i.e. heat per unit time per unit area) during the time interval between the initiation of the flash and the time a selected surface of the sample reaches a predefined temperature. At least one time-temperature characteristic in the time-temperature history is then compared with objective criteria to evaluate the weld quality.